The number of O-ring failures for the first 23 flights of the US space shuttle Challenger were
0 1 0 NA 0 0 0 0 0 1 1 1 0 0 3 0 0 0 0 0 2 0 1
(NA means not available { the equipment was lost). Make a table of the possible categories. Try to find the
mean. (You might need to try mean(x,na.rm=TRUE) to avoid the value NA, or look at x[!is.na(x)].)